If you are in the far north or in the southern us the answer is simple.
Cold air return floor or ceiling.
In a heating climate the return duct goes near the floor to draw off the cold air and heat it up.
If the supply ducts are high or in the ceiling then the return air ducts or grills should be low on.
When the air turns on the fan sucks air into the return air vent thus pulling the warm air from the ceiling and cooling it down which keeps the house cool.
In the summer having the cold air returns near the ceiling is great.
The air grille and vent cover selection from grainger includes steel metal and wood return air grilles and vent covers.
Heat rises and cold air stays close to the floor.
A return draws air into a return duct system with negative pressure compared to the space usually via a fixed grille but also often called a return vent or a return intake vent or for some of you old school folks from up north the cold air return.
Find a decorative metal floor register that will match your home or office decor or go with a standard steel grille with white electro coated and powder coated finish.
Heat rises to the top the cold air return is then pulling the coldest air in the room to the furnace this negative air pressure brings the hot air down and gives the room a more consistent temp.
By putting the cold air return on the floor it will vacuum up the cold air on the floor and draw down the warm air from the ceiling.
Registers these typically slatted covers are found in the floor wall or ceiling and their defining feature is a lever that allows you to open or close the air vent to adjust airflow into the space.
They can be placed into staircase cavities stacked closets that run one on top of the other or in stud cavities in the wall.
So turn the cold air return 90 degrees through the wall so that it actually draws the air from the room next to the furnace room or from the hallway of the basement.
The air flows across the ceiling in the hallway towards a larger cold air return that does extend to the basement furnace.
The return vent pulls cold air from the bottom of the room and returns it to the furnace to be reheated and returned as warm air.
You do this and i guarantee you that the second floor is going to be much more comfortable year round.
One way 10 6 ceiling register.
This pulls the air across your body.
One other caution is to have the cold air.
The problem comes when you use both heating and air conditioning.
The return air vent openings need to be on the opposite side of the room so the conditioned air is pulled across the room.
A cold air return is for cold air other wise it would be called just a return.
You can find floor registers in a variety of materials styles and finishes so you can incorporate them as a decorative element that also blends.
If the supply ducts are in the floor then the return air should be located up high.